1. Field of the Invention
This invention relates to a small and thin semiconductor device which is useful for use in a portable device, such as a cellular phone or an IC card.
2. Description of the Related Art
Conventionally, along with the reduction in apparatus size and thickness, thinning-at-back process for reducing wafer thickness is carried out to reduce the thickness of a semiconductor chip. The reduction of the semiconductor chip is performed by a grinding process to mechanically grind at the back of a semiconductor substrate having semiconductor elements, interconnects, etc. formed on a surface thereof (hereinafter, merely referred to as “wafer”), by an etching process to chemically dissolve the backside or by both of those processes. Usually, where grinding is made as a thinning-at-back process, a non-rigid protection film is bonded on the wafer surface so that, through the protection film, the wafer can be urged at its back onto a grindstone. In this state, grinding is performed by rotating the grindstone.
However, as for the wafer thinned by back grinding, fracture is ready to occur in the wafer or semiconductor chips upon handling by a transfer robot, etc. in the subsequent process, such as cutting process to cut the wafer into individual semiconductor chips, or mount process to mount the cut semiconductor chips onto the lead frame. Particularly, nowadays, because the wafer has an increasing its diameter, fracture occurs more readily in the wafer thinned by back grinding.
In order to solve such a problem, the Japanese Patent Unexamined Publication no. JP-A-11-150090 proposes that, a resin film i.e., polyamide or epoxy, is formed on the wafer surface after forming a projection electrode group on a wafer surface, then thermo-set and hardened, thereby using the hardened resin film as a protection film. The semiconductor device manufacturing method described in the JP-A-11-150090 shows that, the wafer is ground at its back after forming a resin film, furthermore, the top region of the projection electrode group is exposed by removing and etching the surface of the resin film, after that, cutting the wafer along scribe lines into individual semiconductor chips. Meanwhile, it also shows to form an insulation protection reinforcing film by plasma CVD process The plasma CVD process is performed over the resin film surface in an area excepting the side surface of the semiconductor chip the back surface thereof and projection electrode surface.
The semiconductor chip fabricated by this method is covered with a hardened resin film in a surface excepting the exposed projection electrode top regions. Accordingly, during grinding the back or cutting the wafer into individual chips, handling can be done favorably without causing fracture in the wafer or chips. Meanwhile, because the semiconductor chip can be mounted by merely connecting the exposed projection electrode top region with the electrode pad of a wiring board, the semiconductor device can be made thinner conspicuously as compared with the structure extending the external terminal by use of wire bonding, etc.
However, the semiconductor device in the above-described publication JP-A-11-150090 remains in a state polished or etched in order to reduce the thickness of the semiconductor substrate at its back, in other words, semiconductor device is exposed at its substrate backside. Consequently, despite fracture is reduced in back grinding or during handling, the following problem cannot be lessened. Namely, during cutting into semiconductor chips called dicing process, small breakages and micro-cracks called chipping as shown in FIG. 4 readily occur in the individual piece peripheries (cutting regions) in the backside of the semiconductor device. Such breakages and cracks possibly lead to conspicuous lowering in semiconductor device reliability. Meanwhile, during mounting the cut semiconductor chips onto a wiring board, etc., in case there is a foreign matter on the backside of the semiconductor substrate, after mounted on the wiring board, stress is easily applied through the foreign matter to the substrate backside where the semiconductor chip is exposed thus readily causing cracks and breakages in the semiconductor chip. Meanwhile, an impact is applied by such an impact to the semiconductor device upon sucking by a transport suction collet of the mounter during mounting the semiconductor device onto a wiring board, etc., thus raising a fear to cause cracks and breakages in the semiconductor device. Meanwhile, there is a possibility that the wafer warps resulting from a difference in thermal expansion/contraction coefficient between the semiconductor substrate and the resin.